1. Field of Invention
Motion quality problems can cause serious image quality degradation and therefore customer dissatisfaction. Identifying these problems involves measuring pixel placement accuracy with high precision. Techniques exist to do this, but they are laborious and require sophisticated and very expensive equipment.
2. Description of Related Art
It is well known that customer satisfaction can be improved and maintenance costs reduced if problems with copiers and printers can be fixed before they become serious enough to warrant a service call by the customer. While current technology exists to enable printers and copiers to call for service automatically when sensors detect certain operating parameters outside of permissible ranges, there is not a very comprehensive manner of detecting incipient system failure or automatically diagnosing when problems with image quality reach a level where human observers perceive a reduction in quality. This is caused not only by the large number of operating parameters that would need to be tracked, but also because these parameters are strongly coupled to one another.
One of the causes of image quality degradation is associated with motion quality (MQ) problems. A MQ problem is considered to be any source of inaccurate pixel placement anywhere on the printed page, and can occur in the process and/or transverse directions. This includes sources of positional error such as, for example: mechanical noise due to rough gears and bearings, drive shaft eccentricity, ROS polygon wobble, rough paper transport, etc. It does not include irregular motion that leads to color errors but not positional errors, such as that caused by development donor roll shaft eccentricity.
Because MQ problems can cause serious image quality degradation and therefore customer dissatisfaction, much effort is being expended in identifying and eliminating these problems. Identifying these problems involves measuring pixel placement accuracy with high precision. Techniques exist to do this, but they are laborious and require sophisticated and very expensive equipment.
From an engineering perspective, it would be preferable if the measurements could be done quickly and economically at the test site. However, access to high-precision measuring equipment at the site is difficult to obtain and cost-prohibitive. Moreover, for self-correcting printing systems, it is essential that the measurements can be done locally. Flat bed scanners are affordable and are already widely used for image quality evaluation. Moreover, in the case of a printer-copier or a multifunction device, a flat bed scanner is already part of the system. However, such flat bed scanners typically have unacceptably large positional errors over large distances, such as across a page. As such, one would not expect such a scanner to provide motion quality measurements over a large surface with much precision. Accordingly, there are problems with existing image quality analysis systems, particularly those used in the field.
There is a need for image output devices, such as printers and copiers, to have systems to identify problems with image quality. Applicants have found that to comprehensively and reliably measure the system performance of a printer or copier, the image quality of the output must be measured. It is most preferable to have such a device self-diagnose these problems.
There also is a need for a relatively inexpensive system and method to determine image quality errors in image output devices while at the site.
One exemplary embodiment of the systems and methods of the invention overcomes such problems by developing powerful diagnosing tools within a digital printer or copier for self-diagnosis and evaluation of image quality. Image quality analysis can be performed to monitor many aspects of the printed output of the printing system. Of particular importance to overall image quality is determination of motion quality errors.
In this embodiment, the system provides: one or more digital (or hardcopy, in the case of a copier) test patterns and one or more pre-printed patterns for providing one or more hardcopy output test images; an input scanner that can scan the hard copy test image to form a digital raster image; and an image quality analysis module that receives information about the position of the digital raster image and produces test results relevant to determination of image quality analysis, particularly motion quality defects.
The input scanner and image quality analysis module may form part of the image output device or may be stand-alone components used to test the device. Optionally, a communication module may be provided that is capable of contacting a service department or a more sophisticated diagnostic module if further analysis or service is necessary, depending on the outcome of the image quality analysis. Alternatively, information relating to motion quality defects may be used by a corrective procedure within the image output device being tested to calibrate the device to correct for detected motion defects.
The systems and methods of the invention allow highly accurate measurements that are robust in determining motion quality errors, even though the scanners being used are relatively low in precision. The motion quality process relies only on relative measurements, which can be performed sufficiently accurate with standard input scanners. The technique can therefore be used for quick, simple, on-site detection and/or correction of motion quality errors in a printer or digital copier without the need for expensive, high precision measuring equipment.
A special test pattern and measurement technique is used to allow highly accurate measurements of motion quality defects in an image output device that prints in monochrome or color. The method has been demonstrated to be accurate and robust using relatively low-resolution CCD-based flatbed scanners, even in spite of their long-range positional errors.